action_loop's until: condition is never evaluated — the loop always runs once

An `action_loop` step must declare `until:` or `while_condition:` — the compiler rejects it otherwise:

```
YAMLCompilerError: action_loop must have either 'until' or 'while_condition'
```

The condition is then never used. Run, hermetically:

```yaml
- id: loop
action_loop:
- action: filesystem
parameters: {action: write, path: "out/{{ iteration }}.txt", content: "x"}
until: "false"
max_iterations: 4
```

Expected: 4 iterations (`until` never satisfied, capped by `max_iterations`). Observed: **1** iteration, one file. `until: "{{ iteration >= 3 }}"` also gives 1. So does `until: "{{ zzz_nosuch_variable }}"` — a name that exists nowhere raises nothing, which is the giveaway: the string is never rendered or evaluated.

`_check_termination_condition` (`control_flow/action_loop_handler.py:392`) is written correctly — it builds an eval context from `loop_context.to_template_dict()` and calls the condition evaluator. Something above it is not reaching that path, or is terminating first.

Consequence for validation: templates in an `action_loop`'s `until:` are dead text. `core/loop_contracts.py` currently validates them in the loop's body scope, which is the right answer *if* the field is ever evaluated, and harmless (no false rejection) if it is not. That choice should be revisited once this is fixed.